This invention relates to a crude cracking process, especially a process which helps to reduce the production of a heavier fraction of the process, i.e. asphaltene and the like. More particularly, it is concerned with the pretreatment of crude before processing to the following unit, that is a hydrostripping process or bottomless refinery. In a conventional topping unit, residue is treated and cooled by steam to stop polymerization, and is drawn off as quick as possible to be fed to a middle tank or to the next processing step. However it is common that C.C.R. carbon and asphaltene have shown an increase during the process of the conventional processing.
In order to improve defects of the conventional process, a new hydrostripping process as described in U.S. Pat. No. 4,424,117 was invented by the present inventor. The invention therein is a hydrostripping process which is the combination of crude oil distillation and hydrotreating of a distillate overhead, wherein crude oil mixed with a large amount of hydrogen is distilled under high temperature and pressure and separated into a distillate overhead to be hydrotreated, and a heavy residue. Crude oil is separated into two fractions, a lighter fraction and a heavier fraction. The lighter fraction may be charged directly to the following HDS unit with accompanied hydrogen, while no treatment of the heavier fraction is proposed in the invention of U.S. Pat. No. 4,424,117.